V-nail "stack creep"

[Rick Granick]

I have a 4-year-old AMP U-300 underpinner. It works great and I take good care of it. Lately I've noticed that sometimes the stack of v-nails will "creep" up in their clamp at the pushrod end as the machine is being used. If they get to a certain point, the stack doesn't get enough direct pressure to keep the first nail in firing position. Pushing the back of the stack down flat with my finger solves it, but I'm trying to figure out why this is happening. These are 10mm AMP-branded v-nails.

Rick

 

[Jim Miller]

Just guessing..
Has the pusher block worn to the point that it is loose or has a bit of vertical movement? If so, then maybe the surface in contact with the v-nails is slightly angled enough to allow the v-nails to slide up under pressure. Maybe you could check that by removing the v-nails, turning off the air, and twiddling it with your fingers.

 

[tedh]

Maybe as the pressure drops, the nails start climbing. Or just not enough pressure on the clamp to begin with.